In the field of gas turbine, engines it is known that extended length tubes are used to provide various fluids such as fuel, oil. and air, etc. to many components of the engines. Additionally, major systems of the engines include extensive use of tubes for delivering and controlling fluids. Such tubes are typically constructed of thin wall and/or small diameter tubing of nickel alloys and other durable aerospace materials. Typically such tubes include ends that are attached to other engine components, such as manifolds, fuel spray bars, etc., through welds, brazes, tube connectors, fittings, etc. Often, the tubes are integrated within complex gas turbine engine operation systems during manufacturing and assembly of the systems, and are not simply secured between two engine components. An exemplary engine system using integrated oscillating tubes includes combustion fuel nozzles or fuel spray rings that may have multiple and/or complex oscillating tubes that have differing connections on opposed ends of the
As a result of typical geometries of such tubes that commonly have long spans, long aspect ratios, and small diameters, the tubes are susceptible to high-cycle fatigue. In other words, in a normal operating cycle of a gas turbine engine, the engine generates very high frequency vibrations or oscillations as a result of rotation of compressors, turbines as well as interactions with other the engine system as a whole. These forced vibrations and related acoustics or atmospheric waves result in high frequency oscillations within the tubes. The high frequency vibrations are typically measured in Hertz (“Hz”, meaning cycles per second) and may range from 60 Hz (at sub-idle of a gas turbine engine) to 600 Hz (at high-speed operation) and may range as hick as 2,000 Hz. (For purposes herein, the phrase “oscillating tube” is to mean that a tube is subject to between about 60 Hz and about 2,000 Hz.)
Efforts have been undertaken to protect tubes that transfer critical fluids in complex machinery. For example, U.S. Pat. No. 7,309,533 to Zheng et al. that issued on Jul. 15, 2008 discloses use of a protective sleeve around brake tubes and fuel lines for automobiles. Such a sleeve consists primarily of a polyvinylidene fluoride polymer and related complex resins. However, the coating or sleeve was developed to provide the tube by providing resistance to chemical damage, mechanical impact, corrosion and heat stresses. Therefore, the Zheng et al. sleeve encases an entire tube. U.K. Patent Application bearing Publication No. GB 2080474A that was published on Feb. 3, 1982 discloses a fuel line in a gas turbine engine having a slightly larger pipe surrounding the fuel line to produce a gap for collecting any fuel passing out of the fuel line. To protect and lubricate the fuel line from mechanical damage from the outer-larger pipe during assembly, bending and usage, the inner fuel line is coated with a thick layer of polytetrafluoroethylene. As with Zheng et al., however, this coating is for protecting the inner fuel line and/or an interior of the outer pipe, and therefore covers the entire fuel line or the entire interior surface of the outer pipe. While such critical fluid transmitting tubes are known to have been covered with a polymer for the above described protection, to achieve their goals, such coverings require coating an entire tube from end to end. Additionally, such a complete tube coating presents serious challenges to covering any such oscillating tubes that are pre-assembled or integrated within complex systems of the engine.
Therefore, there is a need for a coating applicable to oscillating tubes that may be efficiently applied to the tubes while minimizing costs and labor requirements in applying the coating, and wherein the coated tube minimizes disruption in assembly and usage of the tube.